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From Phil Steitz <>
Subject Re: [math] Backsolve and Frontsolve
Date Wed, 20 Jul 2011 05:54:00 GMT
On 7/19/11 9:55 PM, Greg Sterijevski wrote:
> Hello,
> I was working on some regression issues when I stumbled into the need to
> solve a system like
>   R y = b or R'y = b.
> R is an upper or lower triangular, b is a vector.
> Does this functionality exist? If not, can I add it? And where?

As Ted pointed out, you may be able to somewhat awkwardly get what
you need from either the QR or LU decomp embedded Solver
implementations.  If you have the need, itch and time, I would be +1
to cleanly encapsulate direct back/front solving methods (with the
appropriate zoo of double[] and matrix operands - see the
DecompositionSolver interface) into either a DirectSolver class or
as utility methods added to MatrixUtils.  The latter might make
replacement of the (duplicate) impls in the decomp solvers and other
applications easier.  Others may have different / better ideas on this.

> Thanks,
> -Greg

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